Elongated bead weld method for improvement of fatigue properties in welded joints of ship hull structures using low transformation temperature welding materials

To improve the fatigue properties in the welded joints of high strength steels, we developed an elongated bead method for low transformation temperature (LTT) welding materials. The proposed method intensifies the compressive residual stress and reduces the stress concentration. We investigated the length of the elongated bead in the boxing fillet portion of the gusset front, the effectiveness of inexpensive LTT wires with low Ni content and the potential applicability to repair welding. The most effective welding method, overlay of the elongated bead LTT weld metal on the conventional boxing fillet weld metal, extended the fatigue lifetime of the boxing fillet by seven to ten times. Residual stress distributions in joints welded with low-Ni metals of different martensite start temperatures (Ms) as well as the stress concentration in weld joints formed from elongated beads with different lengths were investigated in finite element simulations. Residual stress of weld and its toe was decreasing as the Ms of weld metal was lowering and the most compressive residual stress was obtained for weld metal with Ms temperature of 184 °C. The stress concentration reduces by about 30% of fatigue load, and the residual stress decreases down to compressive one of −685 MPa for the LTT overlay welding elongated bead treatment.